Joint analog and digital interference cancellation in wireless systems

ABSTRACT

An apparatus for joint analog and digital interference cancellation includes a receiver configured to receive an analog reference interfering signal on a reference path, and a sum of an analog interference signal and an analog signal of interest on an antenna path. An analog interference canceller may be configured to produce an analog partially interference-cancelled signal using the analog reference interfering signal and the sum of the analog interference signal and the analog signal of interest. A first analog-to-digital converter may be configured to digitize the analog reference interfering signal to produce a digital reference interfering signal. A second analog-to-digital converter may be configured to digitize the analog partially interference-cancelled signal to produce a digital partially interference-cancelled signal. A digital interference canceller may be configured to produce an interference-cancelled signal using the digital reference interfering signal and the digital partially interference-cancelled signal.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under W15P7T-12-C-A317awarded by the U. S. Army (Army Contracting CMD-APG).

FIELD OF THE INVENTION

The present invention relates to a system and method for joint analogand digital interference cancellation for wireless communications,thereby improving communication in the presence of interfering signals.

BACKGROUND

As wireless communication systems often require the ability tocommunicate in the presence of strong interfering signals, they employ,for example, “full-duplex” operations in the commercial domain andinterference excision in military applications. These techniques rely ona copy of the interfering signal being available in real-time, whichenables the cancellation (or subtraction) of the interference, incontrast to classic, passive interference-nulling techniques thatpurport to reduce the level of unknown interference. The presentinvention is part of the class of active interference cancellationtechniques, employing joint analog and digital interference cancellationto improve communication in the presence of interference.

SUMMARY

Embodiments of the present invention are directed to methods andsystems, including computer program products, for joint analog anddigital interference cancellation in wireless communication systems. Forexample, in one embodiment, a method for joint analog and digitalinterference cancellation comprises receiving an analog referenceinterfering signal on a reference path; receiving a sum of an analoginterference signal and an analog signal of interest on an antenna path;producing an analog partially interference-cancelled signal via analoginterference cancellation using the analog reference interfering signaland the sum of the analog interference signal and the analog signal ofinterest; digitizing the analog reference interfering signal to producea digital reference interfering signal; digitizing the analog partiallyinterference-cancelled signal to produce a digital partiallyinterference-cancelled signal; and producing the interference-canceledsignal via digital interference cancellation using the digital referenceinterfering signal and the digital partially interference-cancelledsignal, wherein the analog reference interfering signal may bepropagated through a transmission medium to produce the analoginterference signal, and wherein the analog interference cancellationand the digital interference cancellation may be agnostic to thestructure and parameters of the analog reference interfering signal.

These illustrative embodiments are mentioned not to limit or define thelimits of the present subject matter, but to provide examples to aid inthe understanding thereof. Illustrative embodiments are discussed in theDetailed Description, and further examples are provided there.Advantages offered by various embodiments may be further understood byexamining this specification and/or by practicing one or moreembodiments of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of representative prior art in activeinterference cancellation techniques that employ cascaded analog anddigital interference cancellation stages.

FIG. 2 is a block diagram of an embodiment of the joint analog anddigital interference cancellation unit for wireless systems.

FIG. 3 is a block diagram of another embodiment of the joint analog anddigital interference cancellation unit for wireless systems.

FIG. 4 is a block diagram of yet another embodiment of the joint analogand digital interference cancellation unit for wireless systems.

FIG. 5 is a flow chart for a method for joint analog and digitalinterference cancellation, according to an embodiment of the presentinvention.

FIG. 6( a) is a block diagram of a system comprising the joint analogand digital interference cancellation unit according to an embodiment ofthe present invention.

FIG. 6( b) is a block diagram of a system comprising the joint analogand digital interference cancellation unit according to anotherembodiment of the present invention.

Like labels are used to refer to the same or similar modules in thedrawings.

DETAILED DESCRIPTION

Communication in the presence of interfering signals via activeinterference cancellation has been previously studied in the context offull-duplex communication, wherein the transmitter is co-located withthe receiver, and simultaneous transmit and receive (STAR) is required(see, for example, Bharadia et al. “Full duplex radios,” Proc. ACMSIGCOMM, August 2013, pp. 375-386). FIG. 1 is a block diagram of priorart that is representative of full-duplex communication in STAR systemsas described in the aforementioned reference. The prior art receives thesum of a signal of interest and an interference signal on a receiveantenna and attempts to cancel the interference signal.

In particular, as shown in FIG. 1, the analog canceller receives the sumof the signal of interest and the interference signal, and first uses ananalog reference interfering signal, which is obtained from the analogportion of the interference source, to cancel out the interferencesignal. The resulting partially interference-cancelled signal is thendigitized. In the subsequent digital canceller stage, the interferencesource symbols, which are obtained from the digital portion of theinterference source, are used to cancel the remnants of the interferencesignal in the partially interference-cancelled signal, yielding theinterference-canceled signal. The analog and digital cancellers achieve110 dB of cancellation and eliminate self-interference to the noisefloor.

FIG. 1 depicts a paradigm wherein reference signals from distinctportions of the interference source are employed for the cascaded analogand digital cancellation stages. The analog canceller uses an analogreference interfering signal that may be tapped before transmissionthrough the antenna, whereas the digital canceller uses an interferencereference signal based on interference source symbols, which areobtained from the digital components of the interference source.

The present invention, described in the various embodiments herein,employs a distinct architecture in comparison to that depicted in FIG. 1for the full-duplex STAR system. In contrast to using both an analogreference interfering signal and a digital symbol stream for thetwo-stage cancellation process, the present invention employs only theanalog reference interfering signal for analog interferencecancellation, and digitizes this signal for use in the digitalinterference cancellation stage.

FIG. 2 depicts an embodiment of the joint analog and digitalinterference cancellation system 200 for wireless communications. Thejoint analog and digital interference cancellation (JADIC) unit 205 mayreceive two inputs: (1) the reference interfering signal and (2) the sumof a signal of interest and an interference signal via antenna 210. Theinterference signal may be the result of propagating the referenceinterfering signal through a transmission medium. In an embodiment, thetransmission medium is an over-the-air channel that may comprisemultipath components, and the reference interfering signal may beobtained via a local tether. The reference interfering signal may beprovided by a physical wire or link connecting the amplifier output ofthe interference source 206 and the receiver portion of the JADIC unit205. In another embodiment, the transmission medium is full-duplexhardware, such as a circulator, which may distort the signal to somedegree, for instance, by adding multipath.

The reference interfering signal and the sum of the signal of interestand the interference signal are input to the analog interferencecanceller (AIC) 202, which produces a partially interference-cancelledsignal. In an embodiment, the AIC is a single-tap adaptive analogcanceller, which adjusts one or more of the phase, the gain, and thedelay of the reference interfering signal, and subtracts it from the sumof the signal of interest and the interference signal via a signalcombiner. In another embodiment, the AIC may be a multi-tap linearadaptive canceller, which may be used if the transmission medium hassignificant multipath components. Adding taps typically improves thecancellation performance of the AIC, but may be achieved at the expenseof significant complexity since, for example, over-the-air multipathdelays may span several microseconds and are not known in advance.

In this embodiment, the AIC may operate at a radio frequency (RF) or atan intermediate frequency (IF), and subsequent to the analoginterference cancellation, the analog reference interfering signal andthe analog partially interference-cancelled signal may be coherentlydownconverted using mixers 218 and 220, respectively, and localoscillator 222. Coherent downconversion ensures that the phase noisecharacteristics of the two signals are preserved in order to enabletheir cancellation in the digital cancellation stage.

The downconverted analog reference interfering signal and the analogpartially interference-cancelled signal may be digitized usinganalog-to-digital converters (ADCs) 212 and 214, respectively.Parameters of the digital partially interference-cancelled signal may beused to control the AIC via controller 216. In an embodiment, the powerof the digital partially interference-cancelled signal is used todetermine what phase, gain, and delay adjustments should be applied tothe analog reference interfering signal in the AIC.

The digital reference interfering signal and the digital partiallyinterference-canceled signal may be input to the digital interferencecanceller (DIC) 204, which produces the interference-cancelled signal.In an embodiment, the DIC comprises a signal combiner that subtracts thedigital reference interfering signal from the digital partiallyinterference-cancelled signal. In another embodiment, the DIC comprisesfiltering the digital reference interfering signal and then subtractingthe digital filtered reference interfering signal from the digitalpartially interference-cancelled signal to produce theinterference-cancelled signal.

In an embodiment, the filter in the DIC is a linear filter, wherein thefilter taps are based on parameters of the interference-cancelledsignal. In another embodiment, the DIC filter is a non-linear filterwith filter taps that are further based on, for example, the Volterraseries. The Volterra series is a model for the non-linear behavior of asystem, wherein the output of the system at a particular time may dependon the input to the system at all other times.

FIG. 2 depicts an embodiment of joint analog and digital interferencecancellation in wireless systems that is distinct from the prior artshown in FIG. 1. In contrast to using the reference interfering signalfrom the analog portion of the interference source and the interferencesource symbol stream from the digital portion of the interferencesource, only the reference interfering signal from the analog portion ofthe interference source 206 is used for the AIC, and the same signal isdigitized for use in the DIC.

The active interference cancellation architecture depicted in FIG. 2provides at least two distinct advantages over previously studied activeinterference cancellation techniques: the present invention providesbetter matching on transmit non-linearities in both cancellation stages,and cancellation of the phase noise in the digital interferencecancellation stage.

Firstly, using the analog reference interfering signal in the AIC andits digitized counterpart in the DIC provides better matching oftransmit non-linearities between the reference signals and theinterference signal in both of the cancellation stages. Specifically,the interference signal transmitted from antenna 208 may includetransmit non-linearities, but since the analog reference interferingsignal is tapped at the amplifier output of the interference source 206,the same transmit non-linearities may be present in the referencesignals for both the AIC and DIC stages. In contrast, the prior artdepicted in FIG. 1 uses interference source symbols that are obtaineddirectly from the digital portion of the interference source for thedigital canceller; the digital interference source symbol will notcontain any transmit non-linearities that might exist in theinterference signal. Matching the transmit non-linearities typicallyobviates the need for non-linear equalization in the digital processingstage and reduces the complexity of the architecture.

Secondly, coherently downconverting both the reference interferingsignal and the partially interference-cancelled signal after the analogcancellation stage preserves phase noise characteristics of the signals,and enables their cancellation in the subsequent digital cancellationstage. Mismatched phase noises result in a degradation of cancellationperformance of 10 dB (see, for example, Sahai et al., “Understanding theImpact of Phase Noise on Active Cancellation in Wireless Full-Duplex,”IEEE Proc. Asilomar, November 2012, pp. 29-33). The prior art depictedin FIG. 1 uses interference source symbols that are obtained directlyfrom the digital portion of the interference source for the digitalcanceller, and thus do not contain the phase noise characteristics ofthe reference interfering signal.

In an embodiment, the interfering signal source 206 and the JADIC unit205 may be on separate radio platforms, i.e. the interfering signalsource and the JADIC unit may have distinct local oscillators andclocks. The resulting phase mismatch when different oscillators are usedfor the reference interfering signal and the sum of the interferencesignal and the signal of interest can result in the aforementioneddegradation in interference cancellation. This necessitates the need tocoherently downconvert in the analog domain to preserve thecharacteristics so that they may be canceled in the subsequent DICstage.

FIG. 3 depicts another embodiment of the joint analog and digitalinterference cancellation system 300 for wireless communications. Thisembodiment includes some features and/or components that are similar tothose shown in FIG. 2 and described above. At least some of thesefeatures and/or components may not be separately described in thissection. In this embodiment, the reference interfering signal and thesum of the interference signal and signal of interest may bedowncoverted by mixers 318 and 320, respectively, and the AIC mayoperate at IF or baseband. Furthermore, the reference interfering signaland the partially interference-canceled signal may be scaled byamplifiers 322 and 324, respectively, prior to digitization.

In an embodiment, the interference source 306 may be a jammer, whichresults in the power of the interference signal, i.e. the jammingsignal, being several orders of magnitude higher than the power of thesignal of interest. This results in unequal power levels between thereference interfering signal and the partially interference-canceledsignal after the AIC stage, which may necessitate distinct amplificationor attenuation of these signals prior to their digitization.

In another embodiment, the interference source 306 may be a radarsystem, wherein the interference signal may be a radar signal and thesignal of interest may be an unknown communication signal, and there maybe a requirement to communicate simultaneously with radar operation in aSimultaneous Radar and Spectrum Sensing (SRSS) application. Thesimultaneous operation of radar and spectrum sensing may preclude theuse of time-multiplexing, but may be achieved according to an embodimentof the present invention.

As depicted in FIG. 3, the digitized reference interfering signal may beadjusted prior to its use in the DIC. In an embodiment, frequency spursor frequency tones that are identified in the interference-cancelledsignal may be inserted into the reference signal by the spur injectionunit (SIU) 328 to ensure their cancellation in the DIC. The insertion ofthe frequency spurs may be controlled by the SIU controller 330, and maybe based on analysis of the interference-canceled signal.

Frequency spurs are a common artifact of intermodulation distortion,which may be caused by non-linear signal processing, or by hardwarecomponents that are not precisely calibrated or designed. The frequencylocation of the spurs may coincide with the frequency location of thesignal of interest, and thereby prevent its extraction. Eliminatingfrequency spurs, which may be caused by either hardware or signalprocessing methods, ensures that the signal of interest may be extractedfrom anywhere within the frequency band of interest.

FIG. 4 depicts yet another embodiment of the joint analog and digitalinterference cancellation system 400 for wireless communications. Thisembodiment includes some features and/or components that are similar tothose shown in FIGS. 2-3 and described above. At least some of thesefeatures and/or components may not be separately described in thissection. The analog interference canceller 402 in this embodiment maycomprise a gain-phase-delay adjuster 424 that adjusts one or more of thephase, the gain, and the delay of the reference interfering signal, andmay further comprise a signal combiner 426 that subtracts the adjustedreference interfering signal from the sum of the signal of interest andthe interference signal.

The adjustment of one or more of the gain, phase, and delay of thereference interfering signal may introduce nonlinear effects, such asintermodulation products, into the adjusted reference interferingsignal, which may adversely impact the performance of the digitalinterference canceller. To mitigate these nonlinear effects, theadjusted reference interfering signal may be coherently downconvertedvia mixer 428 and local oscillator 422, and may be digitized usinganalog-to-digital converter 432 to produce a digital adjusted referenceinterfering signal. The digital adjusted reference interfering signalmay be used in conjunction with the digital reference interferencesignal and the digital partially interference-cancelled signal toproduce the interference-cancelled signal, wherein the effects of theintermodulation products may have been minimized.

FIG. 5 is a flowchart for a method for joint analog and digitalinterference cancellation, according to an embodiment of the presentinvention. In some embodiments, the order of steps in flowchart 500 maybe changed. Furthermore, some of the steps in flowchart 500 may beskipped or additional steps added.

With reference to FIGS. 2, 3 and 4, the method 500 begins at 510 when ananalog reference interfering signal is received on a reference path. Theanalog reference interfering signal is a copy of the interference and isavailable in real-time. This signal may be supplied to the receiverportion of the JADIC unit via a physical wire or link that is connectedto the amplifier output of the interference source.

The method continues at step 520 when the sum of an analog interferencesignal and an analog signal of interest is received on an antenna path.The analog interference signal may be produced by propagating the analogreference interfering signal through a transmission medium, which may bean over-the-air multipath channel or a circulator. In the general case,the analog interference signal may be a transformed version of theanalog reference interfering signal.

At step 530, the AIC produces an analog partially interference-canceledsignal by subtracting an adjusted version of the analog referenceinterfering signal from the sum of the analog interference signal andthe analog signal of interest. The AIC may comprise a single- ormulti-tap linear adaptive canceller, which may be controlled based onparameters of either the analog or digital partiallyinterference-cancelled signal. In contrast to the prior art, wherein theparameters of the multi-tap analog canceller are determined based on aWiFi preamble sequence of the reference interfering signal, the AIC inthe present invention may be agnostic to the structure and parameters ofthe reference interfering signal.

At step 540, the analog reference interfering signal is digitized usinga first ADC to produce a digital reference interfering signal.

At step 550, the analog partially interference-cancelled signal isdigitized using a second analog-to-digital converter to produce adigital partially interference-cancelled signal. In an embodiment, thefirst and second ADCs are frequency-locked.

At step 560, the DIC produces the interference-canceled signal bysubtracting the digital reference interfering signal from the digitalpartially interference-cancelled signal. In other embodiments, the DICmay further comprise a filter, wherein the filtering digital referenceinterfering signal is subtracted from the digital partiallyinterference-cancelled signal to produce the interference-cancelledsignal.

The filter taps of the filter, which may be a linear or non-linearfilter, may be determined based on parameters of theinterference-cancelled signal. In the prior art depicted in FIG. 1, theparameters of a non-linear digital filter may be determined based on theWiFi preamble sequence of the reference interfering signal. The receivedpreamble samples, which comprise known transmitted symbols, may be usedto determine the filter taps of a non-linear digital filter. In contrastto the prior art, the DIC in the present invention may determine thefilter taps based on parameters of the interference-cancelled signal,and may not rely on preamble or pilot symbols in the digitalcancellation stage. The DIC may not depend on preambles or pilotsembedded in the reference interfering signal, and therefore may beagnostic to the structure and parameters of the reference interferingsignal.

FIG. 6( a) is a block diagram of a system that implements a method forjoint analog and digital interference cancellation in wireless systemsaccording to an embodiment of the present invention. As shown in FIG. 6(a), the system 600 a comprises the JADIC unit 605 that comprises aprocessor 601 and a memory 603. The system 600 a further comprises aninterference source 606 with a transmission antenna 608, and a receiveantenna 610 that feeds the JADIC unit. Herein, transmission antenna 608may broadcast an interference signal from a transmit path, which isreceived on receive antenna 610 along with the signal of interest on thereceive path. In this embodiment, the transmission medium may be theover-the-air channel, which might comprise multipath components.

FIG. 6( b) is a block diagram of a system that implements a method forjoint analog and digital interference cancellation in wireless systemsaccording to another embodiment of the present invention. The system 600b comprises the JADIC unit 605 that comprises the processor 601 and thememory 603. In this embodiment, a single antenna may be used for bothtransmitting and receiving signals, and a circulator 607 connects thetransmit path and the receive path to the single antenna 609. Herein,the transmission medium may be the circulator, which may cause thetransmitting (or interference) signal to be combined with the receivedsignal of interest and sent to the JADIC unit via the receive path.

The processor 601 may comprises component analog and digital processors,and may be configured to execute computer-executable programinstructions stored in memory 603. For example, the component analogprocessor may comprise analog signal processing means for analoginterference cancellation, and the component digital processor mayexecute one or more computer programs for digital interferencecancellation in accordance with embodiments of the present invention.

Processor 601 may comprise a variety of implementations for phaseshifting, switching, delaying, amplification, and attenuation in theanalog domain, as well as a microprocessor, a digital signal processor(DSP), an application-specific integrated circuit (ASIC), one or morefield programmable gate arrays (FPGAs), state machines, or the like.Processor 601 may further comprise a programmable electronic device suchas a programmable logic controller (PLC), a programmable interruptcontroller (PIC), a programmable logic device (PLD), a programmableread-only memory (PROM), an electronically programmable read-only memory(EPROM or EEPROM), or other similar devices.

Memory 603 may comprises a non-transitory computer-readable medium thatstores instructions which, when executed by processor 601, causeprocessor 601 to perform various steps, such as those described herein.Examples of computer-readable media include, but are not limited to,electronic, optical, magnetic, or other storage or transmission devicescapable of providing processor 601 with computer-readable instructions.Other examples of computer-readable media comprise, but are not limitedto, a floppy disk, CD-ROM, magnetic disk, memory chip, ROM, RAM, ASIC,configured processor, all optical media, all magnetic tape or othermagnetic media, or any other medium from which a computer processor canaccess data. In addition, various other devices may includecomputer-readable media such as a router, private or public network, orother transmission devices. The processor 601 and the processingdescribed may be in one or more structures, and may be dispersedthroughout one or more structures.

Embodiments in accordance with aspects of the present subject matter canbe implemented in analog electrical circuitry and/or digital electroniccircuitry, in analog signal processing means and computer hardware,firmware, software, or in combinations of the preceding. In oneembodiment, a computer may comprise a processor or processors. Aprocessor comprises or has access to a computer-readable medium, such asa random access memory (RAM) coupled to the processor.

While the present subject matter has been described in detail withrespect to specific embodiments thereof, it will be appreciated thatthose skilled in the art, upon attaining an understanding of theforegoing, may readily produce alterations to, variations of, andequivalents to such embodiments. Accordingly, it should be understoodthat the present disclosure has been presented for purposes of examplerather than limitation, and does not preclude inclusion of suchmodifications, variations and/or additions to the present subject matteras would be readily apparent to one of ordinary skill in the art.

What is claimed is:
 1. A method for joint analog and digitalinterference cancellation, the method comprising: receiving an analogreference interfering signal from an interference source, the analogreference interfering signal received on a reference path that comprisesan amplifier; receiving a sum of an analog interference signal and ananalog signal of interest on an antenna path; producing an analogpartially interference-cancelled signal via analog interferencecancellation using the analog reference interfering signal and the sumof the analog interference signal and the analog signal of interest;digitizing the analog reference interfering signal to produce a digitalreference interfering signal; digitizing the analog partiallyinterference-cancelled signal to produce a digital partiallyinterference-cancelled signal; and producing an interference-cancelledsignal via digital interference cancellation using the digital referenceinterfering signal and the digital partially interference-cancelledsignal, wherein the analog reference interfering signal is propagatedthrough a transmission medium to produce the analog interference signal,and wherein the analog interference cancellation and the digitalinterference cancellation are agnostic to the structure and parametersof the analog reference interfering signal.
 2. The method of claim 1,the method further comprising: controlling the analog interferencecancellation based on parameters of the digital partiallyinterference-cancelled signal.
 3. The method of claim 1, wherein theanalog interference cancellation comprises: adjusting one or more of aphase, a gain, or a delay of the analog reference interfering signal toproduce an analog adjusted reference interfering signal; and subtractingthe analog adjusted reference interfering signal from the sum of theanalog interference signal and the analog signal of interest to producethe analog partially interference-cancelled signal.
 4. The method ofclaim 3, the method further comprising: digitizing the analog adjustedreference interfering signal to produce a digital adjusted referenceinterfering signal, wherein the digital interference cancellationfurther uses the digital adjusted reference interfering signal toproduce the interference-cancelled signal.
 5. The method of claim 1, themethod further comprising: injecting frequency spurs into the digitalreference interfering signal prior to using the digital referenceinterfering signal for the digital interference cancellation, whereinthe injecting of the frequency spurs is controlled based on parametersof the interference-cancelled signal.
 6. The method of claim 1, whereinthe digital interference cancellation comprises: filtering the digitalreference interfering signal to produce a filtered digital referenceinterfering signal; and subtracting the filtered digital referenceinterfering signal from the digital partially interference-cancelledsignal to produce the interference-cancelled signal.
 7. The method ofclaim 6, wherein the filtering comprises linear filtering.
 8. The methodof claim 6, wherein the filtering comprises non-linear filtering.
 9. Themethod of claim 8, wherein the non-linear filtering is based on aVolterra series.
 10. The method of claim 1, wherein the analoginterference signal is a jamming signal, and wherein a power of thejamming signal is several orders of magnitude greater than a power ofthe analog signal of interest.
 11. The method of claim 1, the methodfurther comprising: scaling the analog partially interference-cancelledsignal by a first gain prior to its digitization; and scaling the analogreference interfering signal by a second gain prior to its digitization.12. An apparatus for joint analog and digital interference cancellation,the apparatus comprising: a receiver configured to receive an analogreference interfering signal from an interference source, the analogreference interfering signal received on a reference path that comprisesan amplifier, the receiver also configured to receive a sum of an analoginterference signal and an analog signal of interest on an antenna path;an analog interference canceller configured to produce an analogpartially interference-cancelled signal using the analog referenceinterfering signal and the sum of the analog interference signal and theanalog signal of interest; a first analog-to-digital converterconfigured to digitize the analog reference interfering signal toproduce a digital reference interfering signal; a secondanalog-to-digital converter configured to digitize the analog partiallyinterference-cancelled signal to produce a digital partiallyinterference-cancelled signal; and a digital interference cancellerconfigured to produce an interference-cancelled signal using the digitalreference interfering signal and the digital partiallyinterference-cancelled signal, wherein the analog reference interferingsignal is propagated through a transmission medium to produce the analoginterference signal, and wherein the analog interference cancellationand the digital interference cancellation are agnostic to the structureand parameters of the analog reference interfering signal.
 13. Theapparatus of claim 12, wherein the analog interference cancellercomprises: a gain-phase-delay adjuster configured to adjust one or moreof a phase, a gain, or a delay of the analog reference interferingsignal to produce an analog adjusted reference interfering signal; and asignal combiner configured to subtract the analog adjusted referenceinterfering signal from the sum of the analog interference signal andthe analog signal of interest to produce the analog partiallyinterference-cancelled signal.
 14. The apparatus of claim 12, whereinthe digital interference canceller comprises: a signal combinerconfigured to subtract the digital reference interfering signal from thedigital partially interference-cancelled signal to produce theinterference-cancelled signal.
 15. The apparatus of claim 12, whereinthe digital interference canceller comprises: a filter configured tofilter the digital reference interfering signal to produce a filtereddigital reference interfering signal; and a signal combiner configuredto subtract the filtered digital reference interfering signal from thedigital partially interference-cancelled signal to produce theinterference-cancelled signal.
 16. The apparatus of claim 15, whereinthe filter is a linear filter.
 17. The apparatus of claim 15, whereinthe filter is a non-linear filter.
 18. The apparatus of claim 12,wherein the analog interference signal is a jamming signal, and whereina power of the jamming signal is several orders of magnitude greaterthan a power of the analog signal of interest.
 19. The apparatus ofclaim 12, the apparatus further comprising: a first amplifier configuredto scale the analog partially interference-cancelled signal by a firstgain value prior to its digitization; and a second amplifier configuredto scale the analog reference interfering signal by a second gain valueprior to its digitization.
 20. A non-transitory tangiblecomputer-readable medium embodying program code executable by acomputing system, the program code comprising: program code forreceiving an analog reference interfering signal from an interferencesource, the analog reference interfering signal received on a referencepath that comprises an amplifier; program code for receiving a sum of ananalog interference signal and an analog signal of interest on anantenna path; program code for producing an analog partiallyinterference-cancelled signal via analog interference cancellation usingthe analog reference interfering signal and the sum of the analoginterference signal and the analog signal of interest; program code fordigitizing the analog reference interfering signal to produce a digitalreference interfering signal; program code for digitizing the analogpartially interference-cancelled signal to produce a digital partiallyinterference-cancelled signal; and program code for producing aninterference-cancelled signal via digital interference cancellationusing the digital reference interfering signal and the digital partiallyinterference-cancelled signal, wherein the analog reference interferingsignal is propagated through a transmission medium to produce the analoginterference signal, and wherein the analog interference cancellationand the digital interference cancellation are agnostic to the structureand parameters of the analog reference interfering signal.